A principal device for changing a speed or a driving force of a vehicle is a drive source such as an engine which is an internal combustion engine and a motor, which are controlled by an accelerating or decelerating operation mechanism such as an accelerator pedal. The driving force can be changed with a manual or automatic transmission and a vehicle speed can be changed accordingly. A brake device cannot increase a driving force but can decrease the driving force to decrease the vehicle speed. On the other hand, the driving force acts so as to cause the vehicle to run and to increase or decrease the vehicle speed and also has a large influence on the turning performance. For example, when the driving force is increased, steering characteristics are changed to tend so as to oversteer or to tend to understeer depending on the structure of the vehicle. Accordingly, in order to stabilize vehicle behavior or to improve running stability, it is preferable that devices capable of changing the vehicle speed or the driving force be controlled in cooperation without being independently controlled.
Therefore, for example, Japanese Patent Application Publication No. 2007-296959 (JP 2007-296959 A) describes a device configured to control a braking force of a brake device and a braking force of a power plant in cooperation. Specifically, in the device described in JP 2007-296959, a target deceleration is calculated on the basis of an amount of pressure or a pressing force against a brake pedal and a brake device is controlled on the basis of the target deceleration. Since a braking force is generated by controlling the brake device and thus the vehicle speed decreases, the transmission gear ratio is controlled so that the deceleration determined on the basis of the vehicle speed reaches the target deceleration. That is, the transmission gear ratio increases.
Japanese Patent Application Publication No. 2006-97862 (JP 2006-97862 A) describes a device configured to generate a deceleration by controlling a transmission and a brake device in cooperation. Particularly, the device described in JP 200697862 A is configured to increase the ratio of the deceleration generated by the transmission when the driving inclination is so-called sport-driving inclination. An example of a device for determining a degree of sport-driving inclination or the driving inclination of a driver is described in PCT International Publication No. 2011/021634. The device described in PCT International Publication No. 2011/021634 is configured to determine driving inclination on the basis of an acceleration (combined acceleration) obtained by combining a longitudinal acceleration and a lateral acceleration of a vehicle. A device that controls a driving force on the basis of determined driving inclination is described in Japanese Patent Application Publication No. 2007-297958 (JP 2007-297958 A). In the device described in JP 2007-297958 A, when it is determined that the sport-driving inclination is strong, the driving force in an accelerator-OFF state at the time of entering a corner is controlled to generate a higher deceleration in comparison with a case where the sport-driving inclination is weak.
However, the device described in JP 2007-296959 A can achieve a target deceleration using the braking force of the brake device and a so-called engine braking force based on the transmission gear ratio, but the target deceleration is calculated on the basis of a amount of pressure applied to the brake device such as an amount of pressure or a pressing force. Accordingly, when the amount of pressure applied to the brake device performed by a driver is insufficient at the time of a vehicle's entering a corner and the brake device is changed to a brake-OFF state during running in the corner, the deceleration becomes insufficient. For example, the amount of pressure applied to the brake device may be insufficient depending on the structure of the corner, due to the driver's misunderstanding of the vehicle speed, or the like, or the operation on the brake may be released to change the brake device to the brake-OFF state when the vehicle speed is satisfactorily or excessively decreases during running in the corner depending on the road structure or due to an excessive or deficient amount of pressure applied to the brake by the driver. In this case, since the target deceleration is calculated on the basis of the deficient amount of pressure applied to the brake, the engine braking force generated depending on the transmission gear ratio after the brake is changed to the brake-OFF state is based on the deficient target deceleration and thus the deceleration becomes deficient. As a result, the vehicle may depart from a target turning line in the corner and it is then necessary to operate the steering wheel or the accelerator so as to correct the departure. Accordingly, there is a possibility that the vehicle will become difficult to drive or the drivability will degrade.
On the other hand, as described in PCT International Publication No. 2011/021634, when the driving inclination is determined and the determination result is reflected in control of the driving force or the steering characteristics of the vehicle, it is possible to perform a control in consideration of the driver's intention and to achieve vehicle behavior intended by the driver. Such driving inclination can be employed for controlling the driving force at the time of running in a corner as described in JP 2006-97862 A or JP 2007-297958 A, but specific techniques for this case or techniques applicable to practical use have not been satisfactorily developed.